Multi-tier power supply for audio amplifiers

ABSTRACT

Techniques for providing multiple power supplies in electronic devices are disclosed. According to one aspect of the present invention, an appropriate power supply is provided only to accommodate a volume setting. In other words, there are at least two power supplies, one with a low voltage and the other with a high voltage. The high voltage power supply is only applied when there is a need to accommodate a volume setting. Thus the power consumption of the amplifiers is well controlled. As a result, the designs of the device and heat dissipation therein can be simplified and lowered in cost.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is generally related to the area of consumer electronics.In particular, the invention is related to method and apparatus forautomatically coupling an appropriate voltage or power supply to anaudio amplifier in a system in responding to a volume so as to increasethe efficiency of the system.

2. The Background of Related Art

An electronic amplifier is a device for increasing the power of asignal. It achieves this amplification by taking power from a powersupply and controlling the output to match the input signal but withgain. An idealized amplifier may be said to be “a piece of wire withgain”, as the output is an exact replica of the input, but larger.

Many electronic devices usually contain one or more amplifiers toenergize audio signals before the audio signals are sent to speakers forsound reproduction. Ideally, the more amplifiers there are, the betterthe sound can be reproduced from the audio signals. Practically, thereare many limitations in a device that limit the use of the amplifiers orpower supplies. Examples of these limitations include physicaldimensions, weight, costs, power consumption, and heat dissipation.Depending on application of an electronic device, appropriate amplifiersshall be designed and operate with appropriate power supply. Thus, thereis always a need for efficient designs in an audio system that producesthe best audio quality possible without going beyond physical designlimitations.

SUMMARY OF THE INVENTION

This section is for the purpose of summarizing some aspects of thepresent invention and to briefly introduce some preferred embodiments.Simplifications or omissions in this section as well as in the abstractor the title of this description may be made to avoid obscuring thepurpose of this section, the abstract and the title. Suchsimplifications or omissions are not intended to limit the scope of thepresent invention.

In general, the present invention pertains to the designs of electronicdevices that reproduce sounds. The electronic devices employ one or moreaudio amplifiers energized by a power supply. According to one aspect ofthe present invention, an appropriate power supply is provided only toaccommodate a volume setting. In other words, there are at least twopower supplies, one with a low voltage and the other with a highvoltage. The high voltage power supply is only applied when there is aneed to accommodate a volume setting. Thus the power consumption of theamplifiers is well controlled. As a result, the designs of the deviceand heat dissipation therein can be simplified and lowered in cost.

According to another aspect of the present invention, a set of supplyvoltages is provided together with a controller. The controller isconfigured to determine which one of the supply voltages shall beapplied to an amplifier in accordance with a volume that may be from avolume setting or volume signal. Depending on implementation, thecontroller may be a circuit or may execute a software module to detectthe volume, and then determine an appropriate supply voltage to beapplied to the amplifier.

To avoid possible audible noise when a low voltage supply is switched toa high voltage supply, a damping circuit is provided in one embodimentto rise from a level of the low voltage supply to a level of the highvoltage supply. Likewise, a damping circuit is provided in oneembodiment to drop from a level of the high voltage supply to a level ofthe low voltage supply when a high voltage supply is switched to a lowvoltage supply.

The present invention may be implemented in many forms includingsoftware, hardware or a combination of both. According to oneembodiment, the present invention is an electronic device that comprisesat least an audio amplifier, a controller, and at least first and secondvoltages. At any time, only one of the voltages is caused by thecontroller to energize the audio amplifier in response to a volume sothat power consumption of the audio amplifier is controlled withoutaffecting audio quality of the audio amplifier.

According to another embodiment, the present invention is an electronicdevice that comprises at least an audio amplifier, a controller and aplurality of power supplies. At any time, only one of the power suppliesis chosen by the controller to energize the audio amplifier in responseto a volume so that power consumption of the audio amplifier iscontrolled without affecting audio quality of the audio amplifier. Eachof the power supplies is designed to have sufficient power wattage topower the amplifier operating under worst case conditions. The worstcase includes increased loading from a speaker and/or additional demandfor power from high-energy signals like a square wave or severelyclipped sinewave.

Other objects, features, and advantages of the present invention willbecome apparent upon examining the following detailed description of anembodiment thereof, taken in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 shows an exemplary configuration in which the present inventionmay be practiced;

FIG. 2A shows an exemplary functional block diagram of using multiplepower supplies to energize an amplifier;

FIG. 2B shows a chart of N supplies, each corresponding to a volume;

FIG. 3A shows one embodiment employing two power supplies alternativelyto energize an amplifier;

FIG. 3B shows that a 14V power supply is immediately replaced by a 36Vpower supply at t1 when a volume goes beyond a threshold;

FIG. 3C shows that a damping circuit is used to gradually rise from thevoltage of the original 14V power supply to a raised voltage of the 36Vpower supply; and

FIG. 4 shows a block diagram of employing one power supply in a priorart system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description of the present invention is presented largelyin terms of procedures, steps, logic blocks, processing, or othersymbolic representations that directly or indirectly resemble theoperations of devices or systems that can be used on networks. Thesedescriptions and representations are typically used by those skilled inthe art to most effectively convey the substance of their work to othersskilled in the art.

Reference herein to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment can be included in at least one embodiment of theinvention. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments mutuallyexclusive of other embodiments. Further, the order of blocks in processflowcharts or diagrams representing one or more embodiments of theinvention do not inherently indicate any particular order nor imply anylimitations in the invention.

Referring now to the drawings, in which like numerals refer to likeparts throughout the several views. FIG. 1 shows an exemplaryconfiguration 100 in which the present invention may be practiced. Theconfiguration may represent, but not be limited to, a part of a soundreproducing device or system, a television set or a home theater system.

To facilitate the understanding of the present invention, it is assumedthat the configuration 100 represents an audio player 110 configured toreceive an audio source 102 and reproduce sounds therefrom. In oneembodiment, the player 110 is coupled to a network that can be wirelessor wired, and part of a local area network or a wide area network. Theaudio source 102, in either analog or digital form, may be locallygenerated from a source (e.g., a broadcast or a DVD or CD player),downloaded or streamed from another device. As an example, the player110 is connected to three speakers, a left speaker 120, a right speaker130 and a subwoofer 125. In operation, the player 110 receives audiosources 102 as an input, processes the input that is then amplified inone or more amplifiers to drive the speakers 120, 125 and 130, where theamplifiers are energized by a power supply.

The efficiency of an amplifier depends largely on its power supply. Theinefficiency resulting from operating with a high supply voltagemanifests itself as heat in an entire system. The heat generated isundesirable for a number of reasons including: increased powerconsumption, increased heat-sink cost, reduced reliability, reducedbattery life in a portable system, and reduced consumer satisfaction.One of the features, objects and advantages in the present invention isto use multiple supply voltages to energize a power amplifier, so thatan appropriate supply voltage is used at all times.

FIG. 2A shows an exemplary functional block diagram 200 of usingmultiple power supplies 202 to energize an amplifier 204. Depending onimplementation, the multiple power supplies 202 may be individual powersupplies, a single power supply with a number of output voltages, or asingle power supply with variable output voltage. In any case, only oneof the power supplies or voltages is used to energize the amplifier inaccordance with a desired volume (e.g., volume setting or signal volume)or a range of volume.

FIG. 2A shows that there are N power supplies 202, where N is a finitepositive integer (e.g., N=2, 3 or 4). Via a switch 206, one of the Npower supplies 202 is coupled to and energizes the amplifier 204 inresponse to a desired volume, as shown in FIG. 2B. In other words, whena volume is below Volume 1, Supply 1 is used. When the volume goesbeyond Volume 1, Supply 2 is automatically switched on to replaceSupply 1. If the volume continues to increase, a next supply isautomatically switched on until a last supply is used.

In one embodiment, the switch 206 is controlled by a circuit thatdetects the volume and is configured to determine which one of the powersupplies shall be used. In another embodiment, the switch 206 iscontrolled by a controller that executes a software module in responseto a setting of the volume. In yet another embodiment, a software moduleis configured to scan a digital file of a track to create a powerprofile so as to optimize the power selection through the track, use aprofile already generated to optimize the power supply selectionthroughout a track; or dynamically “look ahead” in a digital file(either buffered locally or buffered at the transmitting source) tooptimize the power supply selection throughout the track.

To facilitate the description of the present invention, FIG. 3A showsone embodiment 300 employing two power supplies 302 and 304alternatively to energize an amplifier 308. The power supply 302 isdesigned to have a voltage 14V, and the power supply 304 is designed tohave a voltage 36V. In operation, when the power supply 304 is turnedoff, a diode 306 is on, thus the power supply 302 is applied to theamplifier 308. When the power supply 304 is turned on, the diode 306 isoff, thus the power supply 304 is applied to the amplifier 308. Itshould be noted that the use of the diode 306 is one of the exemplaryswitch mechanisms that may be controlled to switch between two powersupplies. Other examples of the switch mechanisms may include, but notbe limited to, a solid-state switch and a mechanical switch.

In a test of using a setting 400 commonly seen in a prior art audiodevice including a single power supply 402 and one or more amplifiers404, as shown in FIG. 4, it was observed that the internal powerdissipation in the audio device remains relatively large when music isplayed at low volume, resulting in a case temperature in excess of 40°C. in a 25° C. room. In fact, the internal power dissipation changesvery little from playing music at low volume to playing nothing at all.In other words, as long as an amplifier is enabled, the power dissipatedis nearly the same as that when playing music at low volume. Under this“quiet” condition, operating with a fixed 36V power supply, the powerdissipation of the audio amplifier, the 36V power supply, and all otherinternal circuits totals approximately 17.5 W.

Accordingly, using the two-tier power supply approach of FIG. 3A, the14V power supply is used to power the audio amplifier at and below apre-determined volume setting. Beyond this setting, the 36V supply isswitched on and only turned off when the setting is below apre-determined volume. Keeping the 36V power supply off when necessary,there are at least three benefits. First, the power consumption of the36V power supply goes away completely. Second, the power consumption ofthe audio amplifier is reduced, owing to a reduced supply voltage.Finally, the bias power to the 36V control circuit is eliminated,including any control circuitry associated with it. Hence, the totalpower dissipation inside the audio device is reduced from 17.5 W toabout 8 W, a savings of 9.5 W, or more than half of the total powerdissipation.

For the audio amplifier operating with lower power, it is reasonable toassume that its efficiency is approximately given by:

$\eta_{LP} \cong {\frac{P_{O}}{P_{O} + P_{STATIC}}.}$

That is, the low power inefficiency is primarily the result of a staticpower loss. By “static,” it means that this amount of power is consumedby the amplifier regardless of whether it is generating audio or not.With the 14V power supply, the static loss P_(STATIC) can be cutsignificantly, compared with the static loss at 36V. In one embodiment,this loss is reduced from 5.5 W to 2 W. Using this approximation, thepower required by the amplifiers is simply the sum of the static powerloss and the speaker output power

P _(AMP) ≅P _(O) +P _(STATIC)

In order for the two-tier power supply to be a viable solution inreducing thermal issue in a device, the overall system must be seamlessin operation and in transition from one power source to the other andback again. To accomplish this, a power supply must be capable ofproviding the required power under worst-case conditions. Theseworst-case conditions include speaker load, controller volume setting,and audio source content. All of these effects shall be considered andmay occur simultaneously, so that no system should ever experience afault in normal operation. To understand the implications of theserequirements, an understanding of the power requirements of the audiosystem is necessary.

Amplifier Gain determines how much output can be expected from anamplifier for a given input signal amplitude. This gain is defined as aratio of the output voltage between speaker terminals to the inputvoltage to the amplifier, and expressed as:

$A_{V} \equiv \frac{v_{out}}{v_{i\; n}}$

Volume Setting. Each volume setting corresponds to a multiplier,relative to the maximum output. A table is used to set the volume foreach of the possible settings. The table below shows exemplary 100settings:

static const float g_rgfVolTable[g_iVolTableSize] = { 0.0, ..., ...,..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...,..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...,..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...,..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...,..., 0.0398, ..., ..., ..., ..., ..., ..., ..., ..., ..., 0.0891, ...,..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...,..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...,1.0000};The two entries in the left column corresponding to volume settings of60 (0.0398) and 70 (0.0891) are significant in that it is believed thatthe transition from the 14V power supply to the 36V power supply to theamplifiers shall occur in or near this range. The corresponding outputpower for these settings is

P _(O)=2×(0.0398×A _(V) ×V _(in,max))² /Z _(speaker);volume=60

P _(O)=2×(0.0891×A _(V) ×V _(in,max))² /Z _(speaker);volume=70

The factor of 2 in the above formula accounts for right and leftchannels, and therefore the total average output power is calculated.The term V_(in,max) refers to the maximum peak-to-peak input voltage tothe amplifier. The term Z_(speaker) refers to the impedance of thespeaker. It has been assumed in the above calculations that the inputsignal is a sinusoidal waveform.

Worst-Case Conditions. It may be shown that from a power supplyperspective, the worst-case waveform is a square wave, since it consumesthe most power for a given signal amplitude. The power in a square waveis twice that of a sine wave of the same peak amplitude. Therefore, itis necessary to increase the power required by a factor of two for theworst-case waveform. Another way of viewing this same requirement isthat the peak power in a sine wave is twice the average power. Hence,even if the sine waves are considered, the power supply must be capableof delivering twice the average power, if only for an instant.

The impedance of speakers is known to vary over a wide range, as afunction of frequency. An amplifier may be designed to match aparticular speaker, where the impedance, as a function of frequency, isknown. In this case, the amplifier can be designed to optimize the powersupply for that particular speaker. Alternatively, an amplifier may bedesigned to work with a generic speaker, where the impedance, as afunction of frequency, is unknown. In this case, the amplifier isdesigned to function with the worst-case impedance, as a function offrequency. To summarize these contributions into a single formula basedon the above two exemplary settings, the worst-case power requirementfor a given volume setting is given by:

P _(O,WORST-CASE)=2×(0.0398×A _(V) ×V _(in,max))² /Z_(speaker,min);volume=60

P _(O,WORST-CASE)=2×(0.0891×A _(V) ×V _(in,max))² /Z_(speaker,min);volume=70

Where Z_(speaker,min) is the minimum impedance exhibited by the speakerover the frequency range of the amplifier. In addition to the proposedrequirement of providing audio power at low volume settings, a selectedpower supply may also be needed to energize other parts in the device.

The impedance of speakers is known to vary over a wide range, as afunction of frequency. An amplifier may be designed to work with ageneric speaker, where the impedance of the speaker is unknown. In oneembodiment, a power supply selected to deliver the requisite power for aspeaker with impedance in a worst case. For example, if the minimumimpedance in a worst case of a speaker is 2 Ohms over a frequency rangeof 20 Hz to 20 kHz, then the power supply shall be expected to deliverthe requisite power under that condition, and the transition from onesupply voltage to another supply voltage will be selected appropriately.Since a power supply is designed to work with generic speakers, the samedesign must also work for a speaker with the minimum impedance of 8Ohms. However, if a single transition point (e.g., volume=60) is usedfor both speakers, then the power supply would be less efficient for the8 Ohm speaker than the 2 Ohm speaker, resulting in more power loss andincreased heat in the 8 Ohm configuration than could be provided if thesystem was designed specifically to work for the 8 Ohms speaker (insteadof the 2 Ohms speaker).

To address the above inefficiency, a configurable parameter is providedto tune the transition point based on the impedance of the attachedspeakers. This parameter may be determined manually or automatically. Inone embodiment, a user is required to make a selection, e.g., using agraphical user interface or a physical switch to select a value, e.g.,2, 4, 6, 8 Ohms. In another embodiment, a circuit is provided to measurean impedance of the speakers connected to the amplifier. Theconfigurable parameter is then provided to a controller to switch to anappropriate power supply.

FIG. 3B shows that a 14V power supply is immediately replaced by a 36Vpower supply at t1 when a volume goes beyond a threshold. To avoidpossible pop-up noise when switching from one power supply to another,an additional circuit is used according to one embodiment. Such acircuit may be coupled to or implemented in the 36V supply 304 of FIG.3A. FIG. 3C shows that a damping circuit is used to gradually rise fromthe voltage of the original 14V power supply to a raised voltage of the36 power supply. The time (t2-t1) to reach the new voltage level may beadjusted depending on the voltage being raised.

In one embodiment, the power supplies are switched in accordance with anaudio signal. More than one power supply is used and switched inaccordance with the amplitude of an audio signal. If the amplitude islow, a relatively lower power supply is switched on. If the amplitude ishigh, a relatively higher power supply is switched on. As a result, thepower consumption is well controlled. In addition, the designs and costsof heat dissipation can be simplified and lowered in cost.

While the present invention has been described with reference tospecific embodiments, the description is illustrative of the inventionand is not to be construed as limiting the invention. Variousmodifications to the present invention can be made to the preferredembodiments by those skilled in the art without departing from the truespirit and scope of the invention as defined by the appended claim. Forexample, a power supply able to produce continuous varying voltages maybe used. Thus at any time, the power supply may be controlled to producean appropriate voltage to be applied on an amplifier. Accordingly, thescope of the present invention is defined by the appended claims ratherthan the forgoing description of embodiments.

1. An audio player comprising: an audio amplifier; at least first andsecond supply voltages to energize the audio amplifier; a controller todetect a volume for play of an audio track and determine an associatedsupply voltage such that, at any time, only one of the first and secondsupply voltages is selected to energize the audio amplifier in responseto the detected volume.
 2. The audio player of claim 1, wherein thecontroller is to detect a volume and determine an associated supplyvoltage based at least in part on a power profile generated from adigital file associated with the audio track.
 3. The audio player ofclaim 2, wherein the power profile is to be dynamically generated via abuffered digital file.
 4. The audio player of claim 1, wherein thecontroller is to determine an associated supply voltage based on aconfigurable parameter to tune a transition point between the first andsecond supply voltages based on speaker impedance.
 5. The audio playerof claim 4, wherein the configurable parameter is to be determined fromat least one of a setting and a measurement.
 6. The audio player ofclaim 1, wherein the first and second supply voltages are to be providedrespectively by first and second power supplies.
 7. The audio playerclaim 1, wherein the first and second supply voltages are to be providedby a single power supply.
 8. The audio player of claim 1, wherein thefirst supply voltage is coupled to the audio amplifier via a switchingmechanism, the switching mechanism to be turned on to couple the firstsupply voltage to the amplifier when the second supply voltage isdisconnected so that the audio amplifier is to be energized by the firstsupply voltage, the switching mechanism to be turned off to couple thesecond supply voltage to the amplifier when the second supply voltage isapplied so that the audio amplifier is to be energized by the secondsupply voltage.
 9. The audio player of claim 1, wherein the secondsupply voltage is to be higher than the first supply voltage.
 10. Theaudio player of claim 9, wherein the second supply voltage is to beapplied onto the audio amplifier via a damping circuit designed togradually rise from a level of the first supply voltage to a level ofthe second supply voltage.
 11. The audio player of claim 10, wherein atime period to rise from the level of the first supply voltage to thelevel of the second supply voltage is adjustable.
 12. The audio playerof claim 1, wherein the controller is a circuit designed to detect thevolume setting and configured to determine which one of the voltages isto be applied.
 13. The audio player of claim 1, wherein the controlleris configured to execute a software module to determine which one of thevoltages is to be applied.
 14. A computer-readable storage mediumincluding a set of instructions for execution by a processor, the set ofinstructions, when executed, to implement a method to control supplyvoltage provided to an amplifier in a playback device, the methodcomprising: detect a volume setting for play of an audio track by anelectronic audio player; determine, using a controller, an associatedsupply voltage for play of the audio track based on the volume settingand available power supply voltages; and facilitate selection of one ofa first supply voltage and a second supply voltage such that, at anytime, only one of the first and second supply voltages is selected toenergize an audio amplifier of the electronic audio player in responseto the detected volume to play the audio track.
 15. Thecomputer-readable storage medium of claim 14, wherein the controller isto detect a volume and determine an associated supply voltage based atleast in part on a power profile generated from a digital fileassociated with the audio track.
 16. The computer-readable storagemedium of claim 15, wherein the power profile is to be dynamicallygenerated via a buffered digital file.
 17. The computer-readable storagemedium of claim 14, wherein the controller is to determine an associatedsupply voltage based on a configurable parameter to tune a transitionpoint between the first and second supply voltages based on speakerimpedance.
 18. The computer-readable storage medium of claim 17, whereinthe configurable parameter is to be determined from at least one of asetting and a measurement.
 19. The computer-readable storage medium ofclaim 14, wherein the first and second supply voltages are to beprovided respectively by first and second power supplies.
 20. Thecomputer-readable storage medium claim 14, wherein the first and secondsupply voltages are to be provided by a single power supply.
 21. Thecomputer-readable storage medium of claim 14, wherein the first supplyvoltage is coupled to the audio amplifier via a switching mechanism, theswitching mechanism to be turned on to couple the first supply voltageto the amplifier when the second supply voltage is disconnected so thatthe audio amplifier is to be energized by the first supply voltage, theswitching mechanism to be turned off to couple the second supply voltageto the amplifier when the second supply voltage is applied so that theaudio amplifier is to be energized by the second supply voltage.